The present invention relates to vane-type hydraulic motors, and more particularly one in which filtered seawater is used as the high pressure hydraulic fluid. This seawater hydraulic motor is designed for underwater usage by divers performing a variety of tasks with the compact lightweight motor.
Prior art hydraulic motors designed for underwater usage have typically employed oil as the hydraulic fluid. The hydraulic fluid is pumped from a surface craft through an inlet hose down to the diver, and must be returned via a return hose. The need for such supply and return hoses limit the diver's handling of the motor, particularly where heavy surge and strong currents exist. The use of oil as the hydraulic fluid creates logistic problems in requiring shipping and storage of large quantities of oil. Leakage of the oil fluid from the motor contaminates the environment, and leakage of seawater into the motor readily damages the precision motor components.
A variety of vane-type hydraulic motors which utilize oil as the working pressurized fluid are seen in U.S. Pat. Nos. 3,981,648; 2,371,081; and 3,752,609. In each of the above-cited prior art vane-type hydraulic motors, which use oil as the working fluid, a rotor turns within a non-circular cam ring as the sliding vanes mounted in the perimeter of the rotor follow the cam ring in proceeding from the high pressure inlet position to the low pressure outlet position. The vanes are radially slidable within slots provided in the rotor and a spring means may be mounted in the base of the vane to urge the vane radially outward against the cam ring. In U.S. Pat. No. 3,981,648, the structure provides high pressure hydraulic fluid to the base of the vanes within the rotor slots to further urge the vane radially outward against the cam ring. This structure comprises an enlarged slot opening between the inward extending end of the slot and the rotor perimeter and also includes a plurality of fluid supply apertures or ports leading from the pressurized fluid inlet, which ports are aligned with a slot enlargement portion in the rotor. In this prior art reference the motor end plates are sealed to the rotor and cam ring track via O-ring seal means.
In U.S. Pat. No. 3,752,609 flexible seal plates are disposed between the rotor and cam ring and the motor enclosure or body. These flexible seal plates are formed of a bimetallic sheet metal material, such as steel and bronze, with the steel forming a resilient flexible support for the bronze bearing material which is adjacent to the rotor. Apertures are provided through the seal plates to permit high pressure hydraulic fluid to be admitted to the space between the rotor and the cam ring track and also to be admitted to the rotor slots to provide a radially outward force upon the vanes which fit within the slots.
U.S. Pat. No. 2,371,081 shows a tapered vane structure, which the vane side faces having undercut portions toward the lower edge. The taper of vanes and the undercut portion facilitate passage of the pressurized fluid to the base of the vane to further assist in urging the vane radially outward into sliding engagement with the cam ring track.
The design of a vane-type hydraulic motor which utilizes seawater as the hydraulic fluid presents a serious challenge because of the general corrosiveness of the seawater on precision made parts of such motors. The poor lubricity of seawater and a much lower viscosity for seawater than for conventional oil hydraulic fluid contribute to the problem. The generally lower viscosity which seawater exhibits means that all design clearances must be an order of magnitude less than for prior art oil hydraulic fluid motors. The motor is designed so that seawater also acts as the lubricant for wear surfaces.